A typical office chair includes a seat/back assembly which is coupled to a chair base by a mechanism that allows controlled tilting of the seat/back assembly with respect to the base. The base usually has an upright post which carries a lower, stationary housing part of the tilt mechanism. Pivoted to the stationary housing part is an upper housing part that carries the seat/back assembly. The back may or may not be movable with respect to the seat. A spring extends between the two housing parts of the tilt mechanism and normally maintains the parts in a rest position with respect to one another. When a person sitting on the chair leans back, the upper housing part tilts with respect to the lower housing part and the spring is compressed, cushioning the tilting movement. The spring tension is adjustable to vary the degree of cushioning.
CA 2,446,654 discloses a chair spring tension control having a side operated actuator that is accessible to a person seated on a chair fitted with the control. CA 2,301,933 discloses a chair seat tilt lock mechanism.